High-strength compressed fiber product



Patented Sept. 17, 1940,

PATENT oF icE mon-srimuc'rii coivirnns snn FIBER.

, 9 raonocr.

George D; KinggChicagbyand Joseph W. Gill,

I EIm hurst, "Ill.," a ssignrs to- United States GypsumeCompany, Chicago; 111., a corporation of Illinois No Da ina; Application.'July a, 1935,

s i lNo.2a7s4 13Claims. (area-55) The present inventionrelates to a compressed fiber product of relatively high strength and of good resistance to water and moisture II One of theobjects-of the invention is to proo duce a compressed, rather dense fiber product -'whichmaybe, in its preferential form,in the form of a board or 'slab'which may be'u'sed as artificial lumber and which,'by reason or the process used in its manufacture, isjendowed with '10 relatively "great strength and good resistan 'ce to water and moisturef I I A I A further objectof the invention concerns the production of a sheet or'board madefrorn' fibrated wood which has beenjfreassembled or rec'on- 15 stituted into" a coherent, relatively'strong'body by a process involvingith'eproduction; fromf'the fibersofth'e wood itself, of autog'enoulsly formed binders, this being effected at a ',temperature of between 400 and 500 in the absence of "all extraneous; sizing 0I binding material s"; that is to say, the productconsistsof thefreassembled woody fiber which "has been made 'eoherent ."by the influence of heat'andapplied pressure, This product"- is .then given increased strength and resistance tofmoisture and, water'by'being din- 'pregnated' arm -acid p tch, the pitchlthen being hardened within the'intersticesjof the tiOll'lI- pressedproduct means of heat."- 1

' 'A' furtheniobjectoif 'the' invention is to'enhanoe i the'phy'sical strength", {and resistance towater and moisture, of: a lcomp 'sessediwood fiber' prodenot I by a process comprising. the impregnation .of. the product with a I solution comprising a; fatt acid pitch, followed by. baking of the product troduced into the interstices ofthe product and game solvents.

Further 'obiects or the {invent on will t ome apparent from the further description andf'claims hereinbelow,

carrying out the present invention'arelignocel lulosic in character; that isto say, theyareeither wood or-a plant material of "a woody naturefialthough the use or cellulose itself-"in 'fairlypure' form is tobe construed as within th' i o dfthe present invention. However, natural wood i by '50 farth'einost desirable raw material for the purpose of carrying out'the inventioni f I As a suitable wood, it might be mentioned that common] Cottonwood] such assis be found in great abundance along-the lowe'rf regions of the Mississippi River, as in the States of hfl'ssiss'ippi or by any other means.

35 a temperature of from, 28O'to 300',=or thereabout',

so as to harden the material which has been in and Arkansas, forms an excellent raw material. Cottonwood trees may be cut up into logs of suitable size, the bark removed, and the logs then of water to wash away the .fibers as they are stripped from the wood. This process is entirely analogous to the wet grinding process employed in the manufacture of common insulating board such as has been manufactured for many years. alternative method is to break the wood into small pieces and then to fibrate the pieces in a suitable dry-grinding mill, which will form loose fibers of wood. Any other suitablemethocl of flbration may also be employed.

f "In its preferred form the invention is carried out substantially as follows: I

" In-the production, for example, of a slab, board, orfIlike article of artificial lumber, any suitable type of wood, such as 'pine, hemlock; spruce,-

poplar, and particularly cottonwood or the like, is'fibrated by any suitable means. This may be ,a'p Icomplished by triturating, that is, grinding it bymeans of'grindstones in the presence of water, I I I I Care is taken to avoid therernoval ofany of the woody materialother thanfsuchparts thereof as are naturally water soluble. The'flber thus obtained is separated M rthe-water used in the grinding by filtration by nieansofa centrifuge or by means of a Decker filter or other equivalent device well known in ythe' pap'er' industry and in'the manufacturepf I I I The fiber thus obtained'ls then dried, although it is' highly preferable to 35' insulating boards.

Sheet the nicer while in water suspension" by means ofa board-forming machine or Fourdrinierl ,wire into a coherent sheet.

" Thus,"'for example, in making such a sheet the fiber may be'suspended in water with aconcentrat'ionof fiber inmwater'of. about 2% to 3%.

I I V I I II r I I ,Sizingrl'raix'erial,waterproofingmaterial or bind- -The raw materials which may be employedfor :ers of any'kindmay be added) the r m e usualxmanneri II i Thesuspension .of fiber in water is fed. to an Oliver boaragrornung machine, on which it is thickness'from about inch to 1 /2 inches.-

I While-on this machine, it is pressed between for wardly moving belts made of felt or the like, so as to -expr'essthe major part of the free water, yield- ":forined into a conti'nuous mat which may vary in r they are subjected to the next step of the process,

using cottonwood, for examp1e,-.a temperature isthen closed with comparatively light pressure, of say about 50 pounds per square inch,'so' that there is good contact between the heated platens resulting from the thermolytic decomposition of the machine, which, may vary from 8 to 24 feet, and these individual slabs or boards are then continuously transported into a hot air drier which may be of the COe type. In this drier the boards are subjected to a continuous'heated-air drying current until they have been relieved or substantially all of their moisture. I

After the boards have been completely dried, and by this it. should be understood that no free moisture of any kind remains'in the boardsin otherwords, that they are bone-dry and as nearly as possible absolutely free from water in any form,

which consists in placing the boards between the platens of a hydraulic press. The platens of this press are heated, as for example by high pressure steam, so that their surface-and the surface of the caul plates that-are used to protect the platens, have'a temperature-of not lessthan 400 F. and'not' substantially greater than 500 F. In

between 440"and' 470 F. has'been found to be the most satisfactory for rapid, economical, com-' mercial operation. The boards, free from nioisboards ma be treated atone .time. Thepress or caul "platesand the surface of .theboards.

While. thus compressed, the boards will be rapidly heated, by reason ofheat transferred'fromthe heated platens or caul plates..- The press preferably-is kept closed for only a few minutes and is then' opened,'but .the boards are allowed to re- The press is then again closed, this time a'pressure within the range of 500 to 3000 pounds per square inch being applied. The pressure is allowed to remain on with full force for a few minutes, say, three or four, when it is again released forthe purpose of allowing the escape of by that time rather copiously developed gases and'vapors thewood. What appears to be taking place'is-a sort of "cracking" or pyrolysis of the lignocellulosic constituents of the wood with the concomiti I ant formation or developmentof-resin-like or tarlike suhstances which will act as binders to fasten the fibers together. Theintermittent release-of 1 pressure is advisable, as itpermits the escape of.

gases and vapors which have developed and which otherwise, if their quantity became too great, would tend to blister or disrupt the board that is being made; -:After the release of pressureand the escape of gases and vapora'lthe. pressure is pressure (that is, three applications of pressure all-together) will usually be suflicient to, produce a firmly consolidated wood board of, say, fro in V;

inch'to inch' in thickness, dependins updnthethickness of the dry mat which has-been pressed. The board thus made is then removed from the press and even, inthatform would be a commercial article of manufacture havingamodulus of rupture on the order of about pounds per square inch, or higher. In order to endow the pressed board with properties of enhanced tensile strength and reslstanceto' water, the second part of the present process is brought into play. This is as follows:

' The boards, while still hot or (if they have been allowed to cool) preferably having been reheated to a temperature of, say, 200 to 300 F., are immersed in an impregnating solution which contains a fatty-acid pitch. A suitable impregnating bath may have the following composition, yiz.',' 00 grams of fatty-acid pitch and 700 grams ofv a petroleum qilstillate having substantially the characteristics oilkerosene. To obtain additional water-resistance',l a waterproofing substance, such as paramn, maybe added to the solution.

. In the abqveformula the fatty-acid pitch is a substance that is derived from the'residues reinaining after thedistillation of fatty acids, as for example obtained from various oils such as cottonseed oil orfrom animal ste'arin. fatty-acid pitches are dark bro'wn toblacksubstances having many- 0f the characteristics of ordinary coal-tar pitch but with the distinction that theyarescapable'of' becoming substantially insoluble injorg'aniesolvents and become solid and"- substantially ;infusible when subjected to ence of oxygen;

' 'Thejimpre'gnation above-mentioned pitchcontaining solution is preferablyeffectediat a temperature of from between 200 and 250 F.' The time that the boards remain in the impregnating bath may vary from 20 to" lillfminutesin the case of boards inch thick to from 45. to 60 minutes in the. case of boards h inch thick; and intermediate periods for boards betwen -the stated thicknesses. During theiimpregnation}; the boards will I become substantially saturatedwith"thefatty-acid pitch solution, so that win finished condition the boards will contain-from about 3% to 6% of pitch. After..the,boards have been in the impregnating bath for asumcient length. or time, they are lifted therefrom, and-the excess solution is removed from the surfacesof theboards by any suitable means, as for instance. by a squeegee or doctor- .blade; A simple wiping'rnay also be employed to The impregnated boards are'then placed into a tunnel ordrie'r, preferably. on edge and separated from each other; so .asto allowxood access of air, and while in this-drier are subjected to a current .of heated air, preferablyat a temperature of froni'280 to 300 -*-F., ,Orv higher. Care must be-taken," of course, to. avoidusing temperatures so high as to cause possible'ignition of the boards. While. in this. drier; .the,solvent-=-that is,

the kerosene-for example willbecome vaporized, 1

which', depo sited in the interstices of the board andz'onthe flbers thereohiwill render .the board moisture and lwater-resistarit..;: Furthermore, it

and the fatty-acid pitch jyill be converted mm 'a substantially infusible and insoluble substance found that when theprocess has been properly earrie'dbut the strength of the boards will be; very greatly increased. For example, when working .with the above-preferred formula and starting with aboard "having amodulus of.rup

ture of, say, 5000 to 7000 pounds square inch, the finished impregnated and bakedboardswill ordinarily have a modulus-of rupture. of about .8000 to 11,000. pounds per'square'inch. The waterabsorption ofsuch aboard will be on the order vofalpoutfroi nil%- to'14;%'.

temperatures of i'roml250? to 300? F. in the presefthe not boardswith the assure that there'is no excess liquid on the boards.

The fatty-acid pitches may be of, any: desired origin, such as cotton stearin pitch, cottonseed fatty-acid pitch, stearin pitch, or. cottonseedoil foots pitch. All of these are now available as, commercial products at a low cost, and forthis reason the cost of carrying. out the present invention is very low, so that it presents great commercial advantages. v

The products obtained are a. pleasing brown to chocolate brown color and, because of their high modulus of rupture, lend themselvestto many industrial uses. Thus, they may be employed as table tops, wall panels, packing cases,,-backing for signs, partitioning, paneling, and forgeneral cabinet work. Due to their high water'resistance, they may also be employed in certain: outside work. i

A very advantageous way of carrying out the.

present invention is to omit all size orwaterproofing materials when, making, the, original board, it having been found that the final product will thus have greater strength, When operating in the absence of size, it is helpful tousea small amount of an acid-reactingsubstanceor salt in the water in which the pulp, is suspended.

Such a salt may consist of aluminum sulfate,

rial, however, is not absolutely essential, as it hasbeen foundthat equally satisfactory products can be made without it, the main advantage inthe use of the same lying in the .fact that in the pressing operations above described there is less sticking to the press platen than when it is omitted. This sticking maybe overcomeinother better and stronger board or. productisobtained in this way than if the fibers: constituting ,theboard have previously been sized or treated with waterproofing agents. The strength of theunimpregnated board (expressed as modulus of rupture) may thus range frorn 000. tcflQOO pounds per square inch, and afterjlimpregnation' and baking it may be as hig' h as1l' 1,000 pounds, This is a totally new and unexpected-'result.f

Board made with sizing an w terprpcn g agents, when pressed, has ai strength of about; 5000 to 6000 pounds, or about 1000 pounds le ss than that oftheunsized board.

The sized, impregnated and baked board has a strength of about 7000 to 8500 pounds as compared with 10,000 to 11,000 pounds in the case of the impregnated and baked but unsized board.

is 2500 to 3000 pounds more than the sized,

impregnated and baked board. Thus before impregnation and baking. the unsized board has' about a IOOO-pound advantage over the sized board, while after impregnation and baking the unsized board has an advantage of about 2500 to 3000 pounds over the sized board, or as much as two and one-half to three times as great.

As a third alternative, it is to be construed as within the present invention to incorporate a portion of the pitch integrally with the board during its formation. Thus a pitch emulsion It'may be stated that the absence of all sizing mayv be added during the sizing operation of the fibers. The method of doing=this-isdescribed-in detail in the copendingapplicationof-Joseph W.

The process described in. said-Gill applicatio comprises the. fibration of :the ligneous material, as by grinding itz-up in the-presence of .water. by means of the usual pulp stones, the-resulting; pulp suspensionsbeing run into a suitable tank provided with an agitator. I While in;said"tank thepulpsuspensionis treated with a sizing mate,;

amongthe fibers. I A solvent .for, the, pitch isfl preferably added to thepitch to facilitate -its emulsiflcation, After thelpitch and fibers have been mixed in the said tank, a sufficient:quantityv of aprecipitant suchasalum or aluminum sulfate is, addedi to decomposethe rosin soap size. withv the formationin the usual manner- -ofan. insoluble precipitate which deposits. i tsel-fupon the fibers. lhe pitch, that ;hasbeen addedtotthe mixture also -is deposited onthefibers. The; rev, sultant suspensionof treatedfibers is now trans' other mechanically equivalent device, upon; which. it is .formed into a wet mat This mat isthen. slightly compacted ==by being passed tbetween s ee e. r ers; l in th nner we :kmwn-m ferred to a suitable board-forming rn'achine such; as-a Fourdrinier. or Qliverboardcformer, or'

th s-a wh reup n the ul nt d n was are transferred :to a drier, wherein zthey, are dried; w h f m r q it r. substa t y all of e m tur t e n cont ine frhe pi ch. by reasonof the. ten'iperature used einjt he} drier; (250735 LE) ,t becomes. somewhat hardened. ,It,

is generallydesirable subsequently,tostorethej oa d o a td s, m o l ss in Ord r t i flien qrea' e t e ha denin i hetn h-t 1 Instead "of forming the ,board wet, it is possible to'proceed by'first producing dryifibrated wood. as by v grinding the same The .thus produced fibers are then mechanically mixed, with. a small, Y S'ubil mo n l at e b veemaiit phed. ch stances 159 form] fibers having 1 these f substances: s hereib- 'h i u e te fl tl tsiam then stored either hot pr com; to ,allow. theadded,

' er e o i Jthei ta y.

fI' e y mats. adam eithero the,, v describedmeth'ods arethen pressed under the herein-disclosed conditions of heat and pressure, being subsequently impregnated with further quantities of pitch.

We claim:

1. The process of producing a dense compressed fiber product which comprises fibrating wood, suspending the resulting fibers in water and sheeting them into a coherent loose mat, drying the mat, compressing the same at a temperaturejof from 400 to 500" F. to effect bonding of the fibers by autogenously developed binders, impregnating the compressed product thus obtained with a solution containing a fatty-acid pitch, and heating the impregnated product to the said solution wood, suspending the resulting fibers in water and sheeting them into a coherentloose mat;

, drying the mat, compressing the same at a temperature of from-440 totso F. to effect bonding I solvent, and heating the impregnated product of the. fibers by autogeno ly developed binders, impregnating the compressed product thu'sob--; tained with a solution-of tatty-acid 'pitch in a to drive or: the solvent and to harden the pitch.

-3. The process oi' producing .adense compressed fiber product which, comprises fibrating' wood, suspending the resulting fibers in'water thusobtained'with a fatty acid pitch, and heat binders, impregnating the compressed product thus obtained with a fatty-acid pitch, and baking at about 300 F. the impregnated product to harden the pitch. g I

4. The process -of producing a dense. com-.

.pressed fiber product which comprises consolidating wood fibers into a dense coherent'ifnass at a temperature of from 400 to-500 F. to'eflect bonding of the fibers" by autogenously'developed' I .-board which comprises suspending wood or woody binders, impregnating the compressed product ing the impregnated product to harden the pitch. 5.-.-'1'he process oi producing a dense, compressed fiber product which comprises. consolidating w'ood'fibers into a densecoher'ent mass at a temperature or from 4,40 to 460 F. to meet bonding of the fibers by autogenously developed binders, impregnating the compressed product thus obtained with a fatty-acid pitch, and baking-the impregnated product to harden the'pitch.

6. The processor producing artificial lumber from lignocellulosie fibers, which comprises adding a fatty-acid pitch to lignocellulosic fibers,

product to harden the pitch.

7. The process of producing compacting the treated fibers while dry ata tern perature of at least'400'F. for-a time sumcient to cause the formationoi autogenous pyrolytic decomposition products, impregnating the compacted product with additional iatty-acld pitch,

artificial. lumberfrom lignocellulosic fibers which-comprises a'dd ing a waterproofing material and a small amount of atatty-acid pitch to llgnocellulosic fibers,-

about 30071 8..Ihe process. eg m 2,215,945 e which com rites precipitating a ram-ma pitch and a me cresinate upon ligneous fibers, dryingthe resulting mixture until completely iree i'rom moisture, compacting the same ata temperature of not lessthan 400 IE, impregnating the compacted product with a further quantity of fatty-acid pitch, and then heating the product to h'arden the pitch.

-9. The process of producing artificial lumber which comprises causing a fatty-acid pitch and 'a metallic resinate to adhere to ligneous fibers,

producing a loosely compressed but coherent mat from the latter, drying the mat until completely freeiromymoisture, compressing the mat at a temperature of between 400 and 500 E, impreg nating the resulting compressed product with a iatty-acid. pitch and baking the impregnated product. i

10.The process of producing an artificial board which comprises suspending wood or woody fibers in a solution or an acid-reacting substance,

filtering the suspension to form a coherent sheet,

completely drying the latter, compressing'it at a temperature between 400 F. and 500 1". to

:iorm a relatively dense board, impregnating the latter with a solution of a fatty-acid pitch in an organic solvent, driving oi! the solvent,

fibers in' water only, filtering the suspension to vforms. coherent sheet, completely drying the latter, compressing it at' a temperaturebetween 400 F. and 500 F. to form a relatively dense board, impregnating the latter with a solution of a tatty-acidpitch in an organic solvent, drip ing or! the solvent, and baking the board at about 300 F.

12. The process of producing an artificial board which comprises suspending unsized wood or woody fibers merely in water, filtering the suspension to form a coherentisheet, completely the latter, compressing it at a temperasolventpdrivlng 011' the solvent,- and baking the board at about 300 1''. j I 13. The process 01' producing an artificial board which comprises sizing wood or woody fibers while in suspension in water, filtering the 'suspension to form a coherent sheet, completely drying the latter, compressing it at a temperature between 400 1". and 500 F.- to form a relatively dense b'oard, impregnating the latter with a solution of ai'atty-acid pitch in an organic solvent,

drivingoi! thesolvent, and baking theboardat ,ononon nxmo.

I JOBIPHWUGIIL' 

